We previously identified a novel mechanism that directly links the inositol trisphosphate receptor (InsPSR) Ca2+ release ion channel to programmed cell death. We extended our new insights into the biochemical and functional interactions of the InsPSR and anti-apoptotic Bcl-2 family proteins with the discovery of an essential requirement of InsPSR activity to suppress macroautophagy and maintain efficient mitochondrial respiration and normal cell bioenergetics. The InsPSR participates in generation of complex Ca2+ signals that regulate many physiological processes in cells, including, as we have discovered, autophagy and basal metabolism, as well as cell survival and death decisions. The studies undertaken to explore this regulation have led to the development of an important new paradigm regarding the regulation of cellular bioenergetics that involves a ubiquitous pathway involving constitutive Ca2+ delivery from the ER to mitochondria mediated by Ca2+ release through the InsPSR and Ca2+ uptake by the mitochondrial Ca2+ uniporter complex. Although our studies have previously defined many of the features of the InsPSR ion channel, the details of the mechanisms of permeation, gating and regulation of the complex of the mitochondrial Ca2+ uniporter are largely unknown. Our preliminary studies suggest that whereas normal and cancer cells have a similar reliance on constitutive mitochondrial Ca2+ uptake for maintenance of optimal bioenergetics, cancers cells are addicted to it since they cannot survive when it is blocked. The mechanisms that underlie this differential sensitivity between normal and cancer cells remain to be elucidated, with obvious clinical relevance. We will employ biophysical (electrophysiology, optical imaging), biochemical, genetic and cell biological approaches to define the mechanistic and structural basis for the uniporter Ca2+ channel complex. Furthermore, we will define the roles of this complex and the InsPSR as molecular targets for cancer cell growth, by use of metabolomics, cell biological and genetic approaches and in vitro and in vivo mouse models. RELEVANCE (See instructions): The ubiquitous expression of constitutive ER-mito Ca2+ transfer has relevance for many physiological and pathophysiological processes, including cancer. A complete molecular understanding of the Ca2+ uniporter complex and appreciation of how cancer cells are addicted to its activity will provide insights that may lead to therapeutic approaches.